Amid concerns over global warming, and forecasts of both the depletion of non-renewable energy sources and rising power demand, suppliers of energy are increasingly seeking alternative primary sources of energy. One such source of energy is solar energy, and one way of utilizing solar energy is with a solar thermal power plant.
One type of solar power plant comprises a solar field which utilizes a “radiation concentrator collector” which concentrates the solar radiation by focusing it onto a smaller area, e.g., using mirrored surfaces or lenses. In this system, a reflector, which is typically parabolic, receives and reflects (focuses) incoming solar radiation onto a radiation absorber, which is formed as a tube. The tube radiation absorber is concentrically surrounded by a treated glass enclosure tube to limit the loss of heat. The collector system further includes means to track the sun.
The tube radiation absorber is made of metal with a coating having a high solar radiation absorption coefficient to maximize the energy transfer imparted by the solar radiation reflecting off the reflector. A heat transfer fluid (HTF), which is typically a liquid such as oil, flows within the tube radiation absorber.
The thermal energy is transported by the HTF to provide energy to, e.g., a thermal-electric power plant to drive one or more power-generation systems thereof, in order to generate electricity in a conventional way, e.g., by coupling the axle of each of the turbines to an electric generator. One such example of a thermal-electric power plant is a steam-electric power plant, which uses thermal energy provided thereto to produce steam to drive turbines thereof, which in turn drive a generator, thus generating electricity.
Throughout the solar field, the HTF flows within a tube, which is partially constituted by the tube radiation absorber. The entire length of the tube should be designed so as to limit thermal losses therefrom. Along much of its length, it is surrounded by a tube or pipe of a larger diameter, with the space therebetween being evacuated in order to limit heat loss due to convection.